The objective of this research is to study the basic biological processes and mechanisms involved in activation of the fibrinolytic system in health and disease. These studies involve the major zymogen of the system, plasminogen, its mechanism of activation, the structure-function relationships of the enzyme, plasmin, the equimolar plasmin-streptokinase activator complex, diagnostic methods and the development of new thrombolytic agents. In these studies, we will isolate and characterize a number of mammalian and avian plasminogens, and separate their isoelectric forms. We will determine the physical and chemical differences between the isolated isoelectric forms of each species of plasminogen. The plasmin-derived heavy (A) and light (B) chains of each species of plasminogen will be separated and characterized. NH2-terminal and COOH-terminal sequences will be determined for each of the plasminogens and plasmin-derived heavy (A) and light (B) chains. This should permit us to establish a general mechanism for activation of all mammalian species of plasminogens. The equimolar plasmin-streptokinase activator will be prepared from those plasminogen species which are readily activated by streptokinase. The molecular events occurring in the formation of the equimolar activator complex will be studied and the plasmin and streptokinase components of the complex isolated and characterized. We will continue our studies on the structure-function relationships of the enzyme and probe the components of the active center of the enzyme. We will determine the phylogenetic relationships of the zymogen and enzyme in all mammalian species. The primary structure of the heavy (A) and light (B) chains will be determined and finally the total primary structure of the zymogen elucidated. New diagnostic methods for studying the fibrinolytic system will be developed in order to study this system in health and disease. Finally, new thrombolytic agents will be developed starting with the equimolar plasmin-streptokinase activator complex.